Non-polymeric peptizers for silver halide suspensions

ABSTRACT

Cyanine and azacyanine dyes are used as non-polymeric peptizers in dispersions of silver halides.

Wmted States Patent 1 1 [111 ,850,645

Herz et a1. 1 Nov. 26, 1974 [54] NON-POLYMERIC PEPTIZERS FOR SILVER 2,441,529 5/1948 Brookcr et a1 96/140 HALIDE SUSPENSIONS 2,573,178 12/1951 Derbyshire 61 a1. 96/139 3,130,197 4/1964 Seefelder et a1. 96/139 [751 Inventors: Arthur Herman Herz; David Frank 3,496,065 2/1970 Russell 96/94 R x OBrien, both of Rochester, NY. 3,620,737 11/1971 Etter et a] 96/363 g ee Eastman o ak Company, 3,697,282 10/1972 Rlester et a1 96/139 Rochester, NY. OTHER PUBLICATIONS Filed? 14, 1973 Harrow'et a1; Laboratory Manual of Biochem. 1960, [211 App}. NO; 388,316 W. B. Saunderg Co., Phi1a., pages 70-71.

Primary Examiner-David Klein [52] CL g 7 Assistant ExaminerAlfonso T. Suro Pico 511 lm. c1 G036 1/24, 603C 1/00 WW/13mm Thomas [58] Field of Search 96/139, 140, 94 R, 114.7,

96/67; 195/4 [57] ABSTRACT 56] References Ched Cyanine and azacyanipedyes are used as non- UNITED STATES PATENTS polymerlc peptlzers 1n dlsperslons 0f sllver halldes.

2,030,050 5/1937 Kendall 96/139 16 Claims, N0 Drawings NON-POLYMERIC PEPTIZERS FOR SILVER HALIDE SUSPENSIONS BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to photography and more particularly to a process for preparing substantially binderfree silver halide crystals for use in light radiation sensitive photographic elements and to the products prepared thereby.

2. Description of the Prior Art Conventional photographic elements employ a support material coated with a photographic emulsion that typically includes photosensitive silver halide crystals dispersed in a hydrophilic colloid such as gelatin. In many instances, gelatin or another hydrophilic colloid is an advantageous constitutent of a photographic element. The use of a hydrophilic colloid binder to promote adequate adhesion between the photosensitive species and the support, however, can be attended by certain related disadvantages that pertain to various photographic situations. Typical binder colloids absorb light of short wavelengths (e.g., ultraviolet rays); as such, the binder material can determine the short wavelength limit of usefulness for any given photographic element. The presence of such binder colloids operates to impede preparation of high quality, ultraviolet-sensitive photographic elements such as those used in astronomical studies.

Moreover, developing agents are required to penetrate the colloid in order to develop a photographic image on the photosensitive material. Additionally, the hydrophilic colloid tends to attract moisture which can adversely affect the stability and image producing capability of the photographic element. Further, special 35 measures must be taken to insure adequate adhesion between the normally hydrophobic support and the hy drophilic colloid binder. To avoid the use of a colloid binder, it is known to prepare photographic elements having thin, binder-free layers of microcrystalline silver halide coated by vacuum deposition techniques wherein the silver halide crystals are formed in situ on the support. Such coating means. however, require spe-- cialized apparatus to carry out the coating operation in a sealed system under conditions of elevated tempera ture and reduced pressure. Additionally, the binderless, microcrystalline silver halilde layers so deposited are subject both to non-uniform photographic response and to deterioration upon storage, the deterioration generally resulting from such factors as pressurecaused abrasion fog.

It is possible to produce monodispersed and crystalographically defined silver halide dispersions in the absence of polymeric vehicles, but these dispersions are known to be both highly dilute and difficult to reproduce. See, for example, Journal of Colloid Science, Vol. 16, p. 581, (1961 and Journal of Colloid Science, Vol. 19, p. 606, (1964). It is also possible to remove gelatin by enzyme hydrolysis from conventionally prepared monodisperse silver halide-gelatin systems as described, for example, in Journal of Colloid and Interface Science, Vol. 23, p. 277, (1967); British Pat. No. 761,014 issued Nov. 7, 1956; British Pat. No. 811,907

issued Apr. 15, 1959; British Pat. No. 1,115,625 issued 65 SUMMARY OF THE INVENTION The present invention comprises the use of cyanine and azacyanine dyes as non-polymeric peptizers in dispersions of silver halides.

More particularly, the present invention comprises a process for preparing dispersions of silver halides comprising:

A. reacting a water-soluble silver salt with a watersoluble halide in aqueous solution in the presence of gelatin whereby a stable gelatinosilver halide photographic emulsion is formed;

25 B. adding to said silver halide emulsion at least one dye of the structure wherein:

A is nitrogen or Cl o-c) v \il l n is 0, l or 2;

An is an acid anion;

W, X and Y are independently selected from the group'consisting of hydrogen, alkyl radicals, aryl radicals, cycloalkyl radicals and alkaryl radicals; and R and R are independently selected from the group consisting of alkyl radicals, aryl radicals, cycloalkyl radicals and alkaryl radicals; and Z and Z each represents the non-metallic atoms necessary to complete a heterocyclic nucleus containing five or six atoms in the heterocyclic ring;

C. hydrolyzing-said gelatin in the presence of said dye by means of at least one proteolytic enzyme;

D. separating the silver halide and said dye adsorbed thereto, and

E. redispersing said silver halide.

Another embodiment of the present invention comprises the silver halide products prepared by the fore- 60 going process. I

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention provides for the replacement of gelatin in preformed silver halide-gelatin dispersions by simple, monomeric organic compounds which are defined herein as being non-polymeric peptizers. These compounds are adsorbed to the silver halide surface and are not affected by the mild enzymatic hydrolysis conditions which are required for gelatin removal. It is a characteristic property of the present peptizers that they not only prevent the irreversible agglomeration of individual silver halide particles, but also interfere with recrystallization processes (Ostwald ripening) and thus help maintain the dispersity and crystal habit of the original silver halide dispersion. It should be noted that the effectiveness of cyanines as restrainers of Ostwald ripening is known in the art, see E. Moisar Grundlagen der Photographischen Prozesse Mit Silberhalogeniden, Akad. Verlagsgesellschaft, Vol. 2, pp. 627-631; Frankfurt am Main (1968).

The term radiation-sensitive, as utilized herein, is descriptive of chemical species (silver salts) that are activated by exposure to electromagnetic radiation to typically provide latent images that can be intensified by various photographic development techniques to provide visible images. The subject silver salts are radiation-sensitive and include species that are lightsensitive. However, radiation-sensitive" comprehends responsiveness to activating radiation both withinand without the visible portion of the spectrum. In addition to photosensitivity or visible light sensitivity, radiationsensitive refers to the responsiveness of an activatable silver salt species through a wide segment of electromagnetic radiation including, for example, x-radiation, ultraviolet radiation, infrared radiation and the like.

The preformed, radiation-sensitive silver salt crystals prepared according to the practice of this invention include those of the silver halides typically employed in gelatino-silver halide photographic emulsions, such as silver bromide, silver chloride and silver iodide. Additionally, mixtures of these halides are advantageously utilized, as are co-crystals, such as, for example, silver bromoiodide, silver chlorobromide, silver chloroiodide, silver chlorobromoiodide, and the like.

The non-polymeric peptizers employed in the practice of this invention are cyanines, azacyanines and related compounds, all having the structure:

In the foregoing structure, A is nitrogen or wherein n is 0, l or 2 and W, X and Y are independently selected from the group consisting of hydrogen, alkyl radicals, aryl radicals, cycloalkyl radicals and alkaryl radicals. As defined herein, the terms alkyl, aryl," cycloalkyl" and alkaryl include the substituted derivatives thereof such as, for example, alkyl substituted derivatives, halogensubstituted derivatives, sulfonate-substituted derivatives, carboxyl-substituted derivatives, aryl-substituted derivatives and the like. Where alkyl radicals are employed, it is preferred that they have from 1 to 12 carbon atoms and most preferred that they have from one to four carbon atoms, for example, methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, and isomers thereof. Where aryl radicals are employed, it is preferred that they be aryl radicals of from 6 to 12 carbon atoms, e.g., benzene, xylene,'toluene, ethyl benzene, butyl benzene, napthylene, chlorobenzene, chlorotoluene, bromonapthylene, and the like. Among the cycloalkyl radicals that can be employed can be listed: cyclopentane, cyclohexane, chlorocyclohexane, bromocyclohexane, and the like. Benzyl radicals and phenethyl radicals are examples of the aryl radicals which can be employed in the dye structures used in this invention.

R and R in the above dye structure are independently collected from the group consisting of alkyl radicals, aryl radicals, cycloalkyl radicals and alkaryl radicals, which radicals are as defined above for W, X and Y. An represents an acid anion such as hydroxide, chloride, bromide, p-toluenesulfonate methanesulfonate, methylsulfate, ethylsulfate, perchlorate, etc. Z and Z each represents the non-metallic atoms necessary to complete a heterocyclic nucleus containing from five to six atoms in the heterocyclic ring, e.g., thiazole, 4- phenylthiazole, 4,5-diphenylthiazole, 4-( 2- thienyl)thiazole, 4-methylthiazole, benzothiazole, 4-

chlorobenzothiazole, 4-methylbenzothiazole, 4- methoxybenzothiazole, 4-ethoxybenzothiazole, 4- phenylbenzothiazole, 5-chlorobenzothiazole, 5- bromobenzothiazole, S-methylbenzothiazole, 5- methoxybenzothiazole, 5-ethoxybenzothiazole, 5- phenylbenzothiazole, 6-chlorobenzothiazole, 6- bromobenzothiazole, 6-methylbenzothiazole, 6- methoxybenzothiazole, -ethoxybenzothiazole, 4- phenyloxazole, benzoxazole, 5-chlorobenzoxazole, 5- methylbenzoxazole, 5-bromobenzoxazole, 5- methoxybenzoxazole, S-ethoxybenzoxazole, 5-

phenylbenzoxazole, l,3-dialkyl, l,3-diaryl or l-alkyl-3- aryl, imidazoles and benzimidazoles, such as 5-chlorol,3-dialkyl benzimidazoles, 5-chloro- -chloro-l,3- diaryl benzimidazoles, 5,6-dichloro-l,3-dialkyl benzimidazoles, 5,6-dichloro-1,3-diaryl benzimidazoles, 5- methoxy-l,3-dialkyl benzimidazoles, 5-methoxy-l,3- diaryl benzimidazoles, 5-methoxy-l,3-diaryl benzimidazoles, 5-cyano-l,3-dialkyl benzimidazoles, 5-cyanol,3-diaryl benzimidazoles, l,3-dialkylnaphth[ 1,2- d]imidazole, l,3-diarylnaphth[2,l-d]-imidazole, 4- methylselenazole, 4-phenylselenazole, selenazole, benzoselenazole, 5-chlorobenzoselenazole, a-naphthothiazole, B-naphthothiazole, quinoline, 6- methylquinoline, 6-methoxyquinoline, 6- ethoxyquinoline, 6-chloroquinoline, 4- methoxyquinoline, 4-ethoxyquinoline, 4-

methylquinoline, 8-methoxyquinoline, B-methylquinoline, 4-chloroquinoline, 3,3-dimethylindolenine, etc.

In the practice of the process of this invention, substantially complete removal of gelatin is effected by enzyme hydrolysis as described in Weiss, Ericson and Herz, J. Colloid and Interface Science, Vol. 23, p. 277 i967). Any enzymes suitable for the intended purpose can be employed, for example, pepsin, trypsin, papain, ficin, pancreatin, and the like. H. T. Proteolytic Takamine, available from Miles Chemical Company, Elkhart, Indiana, has been found to be particularly effective, and is preferred. The amount of enzyme employed will, of course, be dependent upon the activity of the particular enzyme to be used, but, in general, amounts 'in=the range of from about 0.1 to about 2 grams of enzyme per grams of gelatin will be effective.

It is critical to the practice of the present invention that the non-polymeric peptizer be added to the silver halide prior to hydrolysis of the gelatin with the proteolytic enzyme. When this is done, the resulting silver halide particles, after purification, will be found to have retained their original size and morphology. If the nonpolymeric peptizer is added to the dispersion after completion of the gelatin hydrolysis, the dispersion will contain large agglomerates of silver halide particles whose morphology has changed drastically.

The concentration of the non-polymeric peptizer will vary depending upon the size and morphology of the crystals being peptized and on the special characteristics of the particular peptizer. In general, however, levels of non-polymeric peptizer of about 0.05 to about grams per mole of silver halide have been found to be effective and such levels are preferred.

In some cases, it may be desirable to remove the nonpolymeric peptizer from the silver halide surface. In such instances, peptizing compounds which can be desorbed by acid are particularly useful. Since acidinduced desorption of these peptizers causes rapid agglomeration of the silver halide suspension which cannot be reversed by subsequent neutralization, it will be convenient to deposit the silver halide particles first on a suitable support and then to desorb the nonpolymeric peptizer by the acid wash. The resulting silver halide layers, which contain no organic peptizers, retain their original particle size and crystal habit.

It should be recognized that the non-polymeric peptizers employed in the practice of this invention can be cationic, anionic or zwitterionic depending upon the identity of the groups chosen for R and R. For example, when R =R' alkyl (e.g., --C H then the molecule will be a cationic compound, which upon adsorption to silver halide will increase its positive charge density. If both substituents contain acid residue (e.g., R R (CH;), CO Na) then the organic molecule will be anionic and, upon adsorption, will tend to increase the negative charge at the silver halide/solution interface. A similar increase in negative charge density will be observed when the molecule is zwitterionic (e.g., R C H R (CH SO seeWeiss et al., J. Colloid and Interface Science, 23, 277 (1967).

Accordingly, by choosing an appropriate cyanine or mixture of cyanines, most preferably at levels between 0.05 and 1.0 gram per mole of silver halide, it will be possible to adjust the surface charge and zeta-potential at the silver halide/solution interface to an optimum for controlling the stability of the dispersion and the eventual deposition of the silver halide particles by charge control methods.

Since many cyanines are not only strongly adsorbed, but are also colored and efficient spectral sensitizers, their use as peptizers might be limited if they could not be decolorized or removed from the silver halide system. Both processes can be achieved by protonation. This reversible reaction, which is facilitated in cyanines with basic nuclei such as those derived from quinoline or benzimidazole, .decolorizes the dye so that it is no longer a spectral sensitizer. See Feldman et al., J. Phys. Chem., 72, 2008 (1968). Furthermore, as compared with the dye, the colorless protonation product is weakly bound to the silver halide substrate. Hence, as noted above, adsorbed dye can be readily and irreversibly removed from the silver halide surface by treatment with dilute acid.

The following examples are included for a further understanding of the invention.

emulsion (450 ml. per mole) having 3.5 grams of gelatin per silver mole was added to 1000. ml. of 10' M KBr. A solution of anhydro-S,5',6,6 tetrachlorol, l ',3-triethyl-3 -(3-sulfobutyl)benzimidazolocarbocyanine hydroxide (0.012 g.) in methanol ml.) was added to the dispersion. Sufficient dye was used to give monolayer coverage on the silver bromide. The mixture was stirred at 40C. and an aqueous solution of Takamine (0.5 g. in 150 ml.) was added. After stirring for 2 hours, the mixture was centrifuged for 30 minutes at 750 rpm. The supernatant was poured off and the grains were used in 1,000 ml. 10 M KBr. The centrifuged treatment and redispersal in 10 M KBr was repeated twice and yielded a gelatin-free dispersion of dyed cubic silver bromide in 10' M KBr. Electron microscopic examination of the silver bromide particles gave no indication of agglomeration or clumping or of changes in the perfection of the cubic crystal habit. Part B A sheet of polyethylene coated paper was passed for a few seconds through an aqueous colloidal suspension of boehmite alumina. The paper was rinsed with distilled water to remove excess alumina and was dried at about 25C. This dry paper was then passed for a few seconds through the silver bromide suspension prepared in Part A. The coating was then rinsed again with distilled water in order to remove excess silver bromide and was allowed to dry at 25C. Part C A strip of the treated paper of Part B was exposed through a diffraction grating (360-720 nm) containing a superimposed neutral step tablet, developed for about 5 seconds in Kodak Developer D-l9, held briefly in an acetic acid stop bath, fixed and then washed in running water. The resulting silver image extended to about 600 nm.

EXAMPLE 2 A second coating sample prepared as in Example 1 was rinsed consecutively in two 10" M KBr solutions for one minute, the first solution containing 0.1 M HNO;,. Upon exposing and developing as before, no spectral sensitization was observed and the image formed only in the intrinsic adsorption region of the silver bromide. Similar results were obtained when other acids, such as toluene sulfonic acid, were employed. The results indicated that the dye had been removed and electron micrographs gave no evidence of any morphological changes in the silver bromide substrate which was now free of organic surface impurities.

EXAMPLE 3 was added to the dispersion. This provides a. 50 percent surface coverage of the silver bromide. Results similar to those of Example 1 were obtained.

EXAMPLE 4 The same procedure as in Example I was repeated except that a solution of anhydro--chloro-l,l ,3- triethyl-3 3-sulfopropyl benzimidazolocarbocyanine hydroxide (0.01 l g.) in methanol (150 ml.) was added to the dispersion as the peptizer. Again, results equivalent to those of Example 1 were obtained.

EXAMPLE 5 The same procedure as in Example 1 was repeated except that a solution of anhydro-3-methyl-3-( 3- sulfopropyl)-8-azathiacyanine hydroxide (0.008 g.) in methanol (50 ml.) was added to the dispersion as the peptizer. Again, results equivalent to those of Example 1 were obtained except that the resulting image did not extend past the intrinsic sensitivity of the silver bromide.

This invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.

What is claimed is:

l. A process for preparing dispersions of silver halides comprising:

A. reacting a water-soluble silver salt with a watersoluble halide in aqueous solution in the presence of gelatin whereby a stable gelatino-silver halide photographic emulsion is formed;

B. adding to said silver halide emulsion at least one dye of the structure wherein:

A is nitrogen or l w \X Y n n is 0. l or 2;

An is an acid anion;

W, X and Y are independently selected from the group consisting of hydrogen, alkyl radicals. aryl radicals, cycloalkyl radicals and alkaryl radicals; and R and R are independently selected from the group consisting of alkyl radicals, aryl radicals, cycloalkyl radicals and alkaryl radicals; and

Z and 2' each represents the non-metallic atoms nec essary to complete a heterocyclic nucleus contain ing five or six atoms in the heterocyclic ring;

C. hydrolyzing said gelatin in the presence of said dye by means of at least one proteolytic enzyme;

D. separating the silver halide and said dye adsorbed thereto, and

E. redispersing said silver halide.

2. The process of claim 1 further comprising the step of removing the dye by protonation.

3. The process of claim 1 wherein the dye is present in a concentration of from about 0.05 to about 10 grams per'mole of silver halide.

4. The process of claim 1 wherein the proteolytic enzyme is present in a concentration of from about 0.1

gram to about 2 grams of enzyme per grams of gelattn.

5. The process of claim 1 wherein the proteolytic enzyme is H. T. Proteolytic Takamine.

6. The process of claim 1 wherein the dye is anhydro- 5,5',6,6-tetrachlorol ,l ,3-triethyl-3-( 3-sulfobutyl)- benzimidazolocarbocyanine hydroxide.

7. The process of claim 1 wherein the dye is anhydro- 5-chl0rol ,l ,3-triethyl-3 3-sulfopropyl )ben- Zimidazolocarbocyanine hydroxide.

8. The process of claim 1 wherein the dye is anhydro- 3-methyl-3'-(3-sulfopropyl)-8-azathiacyanine hydroxide.

9. A process for preparing dispersions of silver halides comprising:

A. reacting a water-soluble silver salt with a watersoluble halide in aqueous solution in the presence of gelatin whereby a stable gelatine silver halide photographic emulsion is formed;

B. adding to said silver halide emulsion from about 0.05 to about 10 grams per mole of silver halide of at least one dye of the structure wherein:

A is nitrogen or An is an acid anion;

W, X and Y are independently selected from the group consisting of hydrogen, alkyl radicals, aryl radicals, cycloalkyl radicals and alkaryl radicals; and R and R are independently selected from the group consisting of alkyl radicals, aryl radicals, cycloalkyl radicals and alkaryl radicals; and

Z and Z each represents the non-metallic atoms necessary to complete a heterocyclic nucleus containing five or six atoms in the heterocyclic ring;

C. hydrolyzing said gelatin in the presence of said dye by means from about 0.1 gram to about 2 grams of at least one proteolytic enzyme per 100 grams of gelatin;

D. separating the silver halide and said dye adsorbed thereto, and

E. redispersing said silver halide.

10. The process of claim 9 further comprising the step of removing the dye by protonation.

11. The process of claim 9 wherein the proteolytic enzyme is H. T. Proteolytic Takamine.

12. The process of claim 9 wherein the dye is anhydro-5,5,6,6'-tetrachlorol ,l ',3-triethyl-3'-( 3- sulfobutyl(benzimidazolocarbocyanine hydroxide.

13. The process of claim 9 wherein the dye is anhydro-5-chlorol ,l ,3-triethyl-3'-( 3-sulfopropyl )benzimidazolocarbocyanine hydroxide.

14. The process of claim 9 wherein the dye is anhydro-3 methyl-3-'-(3-sulfopropyl)-8-azathiacyanine hydroxide.

15. A photographic silver halide emulsion prepared by process comprising:

A. reacting a water-soluble silver salt with a watersoluble halide in aqueous solution in the presence of gelatin whereby a stable gelatino silver halide photographic emulsion is formed;

B. adding to said silver halide emulsion at least one dye of the structure wherein:

A is nitrogen or n is 0, l or 2;

An is an acid anion;

W, X and Y are independently selected from the group consisting of hydrogen, alkyl radicals, aryl radicals, cycloalkyl radicals and alkaryl radicals; and R and R are independently selected from the group consisting of alkyl radicals, aryl radicals, cycloalkyl radicals and alkaryl radicals; and Z and Z each represents the non-metallic atoms necessary to complete a heterocyclic nucleus containing five or six atoms in the heterocyclic ring;

C. hydrolyzing said gelatin in the presence of said dye by means of at least one proteolytic enzyme;

D. separating the silver halide and said dye adsorbed thereto, and

E. redispersing said silver halide.

16. A photographic element comprising a support having deposited thereon a silver halide emulsion prepared by a process comprising:

A. reacting a water-soluble silver salt with a watersoluble halide in aqueous solution in the presence of gelatin whereby a stable gelatino-silver halide photographic emulsion is formed; B. adding to said silver halide emulsion at least one dye of the structure wherein:

' A is nitrogen or An is an acid anion;

W, X and Y are independently selected from the group consisting of hydrogen, alkyl radicals, aryl radicals, cycloalkyl radicals and alkaryl radicals; and R and R are independently selected from the group consisting of alkyl radicals, aryl radicals, cycloalkyl radicals and alkaryl radicals; and

Z and Z each represents the non-metallic atoms necessary to complete a heterocyclic nucleus containing five or six atoms in the heterocyclic ring;

C. hydrolyzing said gelatin in the presence of said dye by means of at least one proteolytic enzyme;

D. separating the silver halide and said dye absorbed thereto, and

E. redispersing said silver halide. 

1. A PROCESS FOR PREPARING DISPERSIONS OF SILVER HALIDES COMPRISING: A. REACTING A WATER-SOLUBLE SILVER SALT WITH A WATER-SOLUBLE HALIDE IN AQUEOUS SOLUTION IN THE PRESENCE OF GELATIN WHEREBY A STABEL GELATINO-SILVER HALIDE PHOTOGRAPHIC EMULSION IS FORMED; B. ADDING TO SAID SILVER HALIDE EMULSION AT LEAST ONE DYE OF THE STRUCTURE
 2. The process of claim 1 further comprising the step of removing the dye by protonation.
 3. The process of claim 1 wherein the dye is present in a concentration of from about 0.05 to about 10 grams per mole of silver halide.
 4. The process of claim 1 wherein the proteolytic enzyme is present in a concentration of from about 0.1 gram to about 2 grams of enzyme per 100 grams of gelatin.
 5. The process of claim 1 wherein the proteolytic enzyme is H. T. Proteolytic Takamine.
 6. The process of claim 1 wherein the dye is anhydro-5,5'' ,6,6'' -tetrachloro-1,1'' ,3-triethyl-3''-(3-sulfobutyl)benzimidazolocarbocyanine hydroxide.
 7. The proCess of claim 1 wherein the dye is anhydro-5-chloro-1, 1'',3-triethyl-3''-(3-sulfopropyl)benzimidazolocarbocyanine hydroxide.
 8. The process of claim 1 wherein the dye is anhydro-3-methyl-3''-(3-sulfopropyl)-8-azathiacyanine hydroxide.
 9. A process for preparing dispersions of silver halides comprising: A. reacting a water-soluble silver salt with a water-soluble halide in aqueous solution in the presence of gelatin whereby a stable gelatino silver halide photographic emulsion is formed; B. adding to said silver halide emulsion from about 0.05 to about 10 grams per mole of silver halide of at least one dye of the structure
 10. The process of claim 9 further comprising the step of removing the dye by protonation.
 11. The process of claim 9 wherein the proteolytic enzyme is H. T. Proteolytic Takamine.
 12. The process of claim 9 wherein the dye is anhydro-5,5'' ,6, 6''-tetrachloro-1,1'' ,3-triethyl-3''-(3-sulfobutyl(benzimidazolocarbocyanine hydroxide.
 13. The process of claim 9 wherein the dye is anhydro-5-chloro-1,1'' ,3-triethyl-3'' -(3-sulfopropyl)benzimidazolocarbocyanine hydroxide.
 14. The process of claim 9 wherein the dye is anhvdro-3-methyl-3'' -(3-sulfopropyl)-8-azathiacyanine hydroxide.
 15. A photographic silver halide emulsion prepared by process comprising: A. reacting a water-soluble silver salt with a water-soluble halide in aqueous solution in the presence of gelatin whereby a stable gelatino silver halide photographic emulsion is formed; B. adding to said silver halide emulsion at least one dye of the structure
 16. A photographic element comprising a support having deposited thereon a silver halide emulsion prepared by a process comprising: A. reacting a water-soluble silver salt with a water-soluble halide in aqueous solution in the presence of gelatin whereby a stable gelatino-silver halide photographic emulsion is formed; B. adding to said silver halide emulsion at least one dye of the structure 